Ignition circuit



Filed March 7, 1960 INVENTOR. William J Johns/on Y mam H/s Al/omey United States Patent-"O 3,030,548 IGNITION CIRCUIT William J. Johnston, Flint, Mich, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Mar. 7, 1960, Ser. No. 13,346 4 Claims. (Cl. 315-177) This invention relates to electric ignition systems and more particularly to ignition systems for use with rocket engines and the like, I

The present invention contemplates providing an electric ignition system that includes a capacitor and a circuit element that breaks down to conduction when a predetermined voltage is applied across it. The capacitor and circuit element are connected in such a manner that the circuit element breaks down to complete a work circuit whenever the capacitor is charged to a predetermined voltage.

In circuits of the type described, the capacitor has been charged from a direct current source. This has required the use of one or more rectifiers and in some instances the use of an expensive and cumbersome apparatus such as dynamotors.

It is accordingly an object of this invention to provide an electric ignition system of the type described that is energized directly by alternating current, thus eliminating the need for rectifiers, dynamotors and the like.

Another object of this invention is to provide an electrical ignition system that is powered by alternating current and wherein the sparking rate of the ignition system is a function of the frequency of the alternating current.

Another object of this invention is to provide an electrical ignition system that includes a first condenser, a transformer, a circuit element having a predetermined breakdown voltage and a second condenser; the first condenser, primary winding of the transformer and circuit element being interconnected while the second condenser is connected across the secondary winding of the transformer and across a spark discharge device.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings, the single FIGURE drawing illustrates an electrical ignition system made in accordance with this invention.

Referring now to the drawing, a source of alternating current is designated by reference numeral 10. The alternating current source is connected with lead wires 12 and 14 which form the input leads for the circuit. A resistor designated by reference numerals 16 is connected in series with lead wire 12 and is connected in series with a capacitor designated by reference numeral 18. An ignition coil or step-up transformer designated in its entirety by reference numeral 20 is provided. The primary winding 22 of the ignition coil is connected in series with capacitor 18 and is connected with lead wire 14 as is clearly apparent from the drawing. A secondary winding of transformer 20 is designated by reference numeral 24 and it is seen that this secondary winding feeds a circuit including lead wires 26 and 28.

A circuit element designated by reference numeral 30 is provided which is connected across input leads 12 and 14, one side of which is connected between resistor 16 and capacitor 18. The circuit element 30 has a predetermined breakdown voltage and may be, for example, a gas tube that is filled with inert gases and which breaks down when a predetermined voltage is applied across it. The breakdown phenomena in such a case is actually an arc.

The lead wires 26 and 28, which are connected with secondary winding 24, are connected with a spark discharge device which is designated by reference numeral 32. It will be appreciated that the spark discharge device will be positioned'within an engine so as to ignite the combustible mixture of the engine. A condenser designated by reference numeral 34 is connected across the leads 26 and 28.

In operation of the device, when the lead wires 12 and 14 are energized by alternating current, the condenser 18 is charged during the first quarter cycle of each half cycle of the alternating current. The resistance value of resistance 16 and the capacitance of capacitor 18 are so chosen that the capacitor will attain a charge sufiicient to break down the tube 30 on each half cycle of the alternating current. Thus, where the alternating current applied to leads 12 and 14 is volts R.M.S. or 162 volt peak, the breakdown voltage of the tube is 90 volts R.M.S. or 127 volts peak. Thus, it is clearly apparent that the condenser 18 will be charged and discharged on each half cycle of the alternating current, the condenser discharging whenever the voltage across it attains the predetermined breakdown voltage of gas tube 30.

When the condenser 18 discharges through the gas tube 30 and through the primary winding 22 of ignition coil 20 a high voltage is induced in thesecondary winding 24. This voltage is applied to the condenser 34 and when the condenser has been charged to a value of voltage sufficient to break down the spark discharge device 32, an arc is caused to jump across the spark discharge device.

It can be seen from the foregoing that the sparking rate across spark discharge device 32 will be equal to twice the frequency of the voltage applied to leads 12 and 14. Thus, where 60-cycle A.C. voltage is employed, the sparking rate will be cycles per second.

It is important in the design of this circuit that the RC. time constant of resistor 16 and capacitor 18 be of such a value that the condenser 18 attains a sufficient charge to break down the gas tube 30 during the first quarter cycle of each half cycle of the applied voltage.

While the embodiments of the present invention as herein disclosed constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

l. An ignition system comprising, a source of alternating current, an ignition transformer having a primary winding and a secondary winding, a spark discharge device connected With secondary winding, a resistor, a capacitor, means connecting the primary winding of said ignition coil, said resistor and said capacitor in series and across said source of alternating current, a circuit element having a predetermined breakdown voltage, and means connecting said circuit element across said source of alternating current with one side thereof being connected between said series connected resister and said capacitor, the resistance value of said resistor and the capacitance value of said capacitor having an RC. time constant of such a value that said capacitor attains the predetermined breakdown voltage of said circuit element twice in each cycle of said alternating current.

2. An electrical ignition system comprising, a source of alternating current, a pair of lead wires connected with said source, a circuit element having a predetermined breakdown voltage, a resistor, a first capacitor, an ignition coil having a primary winding and a secondary winding, means connecting said resistor and said capacitor and said primary winding of said ignition coil across said voltage source, means connecting said circuit element across said lead wires with one side thereof being connected between said resistor and said capacitor, a spark discharge device connected with said secondary winding of said transformer, and a second capacitor connected across said secondary winding.

3. An electrical ignition system comprising, a source of alternating current, an ignition transformer having a primary winding and a secondary winding, a capacitor, a series charging #circuit -for said-capacitor including a resister and the primary winding of said ignition transformer, a discharging circuit for said capacitor including the primary winding of said ignition coil and a circuit element having a predetermined breakdown voltage, a spark discharge device, and means connecting said spark discharge device with the secondary winding ofsaid ignition' transformer, said resistor and capacitor having an R.C; time constant of such a value that said condenser discharges through the primary winding of said ignition coil ,at a rate which is a function :of the frequency of :the alternating current source.

4. ignition system comprising, a pair of lead wires adapted to be connected directly across a source of alternating current, an ignition transformer having a primary winding and a secondary winding, a series circuit connectin-g said lead wires and including a resistor, a capacitor and the primary winding of said ignition coil, a circuit element having a predetermined breakdown voltage, and means connecting said circuit element across said lead wires and in parallel with said primary winding and capacitor.

References Cited in the file of this patent UNITED STATES PATENTS 2,030,228 Randolph et a1. Feb. 11, 1936 2,071,573 Randolph et'al. Feb. 23, 1937 2,093,848 Randolph -et a1. Sept. '21, 1937 2,197,114 Rabezzana et al. Apr. 16, 1940 2,497,307 Lang Feb. 14, 1950 2,551,101 Dehenham et-al May 1, '1951 2,651,005 'Tognola Sept. 1, '19'53 

